Stroke, neurodegenerative diseases, brain tumors, respiratory disorders, and the like may cause dysphagia resulting in insufficient control of muscles needed for swallowing. In severe cases, aspiration pneumonia may result. Dysphagia often results from poor control of some muscles in the upper respiratory system. Many muscles in this system are also involved with speech and voice.
In general, swallowing disorders are predominately a human problem because the ability to have highly developed speech is directly related to the much lower location of the larynx (lower compared to the larynx of many animals) which in turn enhances the dangers associated with swallowing. The higher position of the larynx in some animals, in which the larynx is not a highly developed natural speech apparatus, even allows these animals to drink and breathe simultaneously—something which is impossible for human beings.
In humans, at least twelve muscles are involved in the swallowing process. Proper control of their movement is particularly important since the failure of movement may have critical consequences. However, there is no clear understanding of which muscles may predominate or even if proper swallowing requires coordinated contraction of all twelve or more muscles since the swallowing process varies from person to person. For example, the geniohyoid, mylohyoid and digastric muscles are used selectively by different individuals, e.g., some use all three muscles at the onset of swallowing, while others use different pairs. In addition, the temporal association between submental muscle contractions differs across individuals.
Electrical stimulation has been successfully used for controlling weakened muscles/nerves, such as aged or degenerated nerves/muscles, for controlling re-innervating nerves, including synkinetically re-innervating nerves, and/or for providing electrical signals to nerves in order to compensate for hearing deficiencies (e.g., cochlear implant stimulation for providing hearing sensations to deaf people) or to overrule wrong elicited nerve signals.
Various stimulation systems and methods have been proposed to control the upper respiratory muscles used for swallowing, but none of them addresses the elevation of the larynx in order to provide for proper swallowing. For example, Freed et al. describe a non-invasive method and apparatus that continuously stimulates the skin surface to assist patients in initiating a swallow (see, e.g., U.S. Pat. Nos. 5,725,564, 6,104,958, and 5,891,185). In addition, there are systems which cause glottis closure by means of appropriate electrical stimulation (see, e.g., Bidus et al., Laryngoscope, 110:1943-1949, 2000; Ludlow et al., Journal of Artificial Organs, 23:463-465, 1999; and Ludlow et al., Muscle and Nerve, 23:44-57, 2000). In U.S. Pat. Appl. No. 2007/0123950, Ludlow et al. disclose a method and system for synergistic production of muscle movements during speech, swallowing or voice production by moving the hyoid bone and/or parts of the upper airway and/or vocal tract by means of electrical stimulation of at least two different muscles. Ludlow et al. found that neuromuscular stimulation of only two of the muscles yields a large proportion of normal desired movement for the hyoid bone. Further, Ludlow et al. disclose that the muscles involved in swallowing remain at their normal, given locations within a human's body. All of the above cited documents are incorporated by reference herein in their entirety.